Almost every political campaign turns on the personality and positions of one of the candidates. In this year's California Senate race, Gov. Jerry Brown is the one.

After eight years in Sacramento, two failed presidential campaigns and a string of political imbroglios, Brown accumulated a lot more critics than admirers among the state's voters. Brown's failures and foibles have appeared regularly on the TV news -- what the insiders call the "free media." The free media -- what television stations put on their news shows -- is beyond a candidate's control, but "paid media" -- commercials -- can be used by an effective candidate to rebut or exploit stories reported in the free media. That's what's happening this year in California.

Jerry Brown, a smart man and a shrewd campaigner, defines his own campaign. The Brown advertising strategy was logical and its execution was effective. It began with commercials featuring "people" (that is, actors) who intended to vote for the Republican candidate, San Diego Mayor Pete Wilson. When an off- camera announcer informed these voters about some Wilson position they had not previously known and with which they could not agree, they responded: "Maybe I'll have to take another look at Jerry Brown." The announcer concluded by telling the presumably anti-Brown viewers: "Maybe you should take another look at Jerry Brown."

The most important race in this campaign may have been the one between the two camps to determine which of them could first shape the voters' perception of Wilson, much the lesser-known candidate. The Wilson campaign produced a dozen spots trumpeting their man's humanity and his achievements as mayor.

But the free media can be powerful enough to upset the est-planned advertising campaign. Wilson's impolitic public musings about a quasi- voluntary Social Security program and popular election of federal judges hurt the Republican. Brown's radio and TV spots, part of a $4-million buy, pounced on these slips, keeping voters' attention away from the unpopular governor and on his opponent.

Then Brown and his campaign made a serious mistake of their own. Trying to take advantage of Brown's strong support for the proposed nuclear freeze and Pete Wilson's opposition to it, the Brown campaign broadcast a commercial that included brief appearances by Dodgers' third baseman Ron Cey ("I want to keep on playing baseball."); actor Tony Randall ("I just want to go on making people laugh."), and actress Candice Bergen ("I want to keep on doing it all "). Then followed the sound and sight of a nuclear explosion with this narration: "Pete Wilson opposes the nuclear arms freeze. Jerry Brown supports it. Vote for your life. Elect Jerry Brown to the U.S. Senate." With this videotaped piece of McCarthyism of the left, Brown succeeded in putting the spotlight back on himself.

The free media made a major issue of this commercial, and Brown withdrew it within a week. Just as Wilson's free media snafus were grist for Brown's commercials, so Brown's paid media excess rebounded to Wilson's advantage in the free media. Wilson's self-confidence also got a boost from his better-than-expected performance in debates with Brown.

In the negative style of this season, Wilson has used his paid media to remind voters why they didn't like Brown in the first place. A recent Wilson commercial features Brown with his controversial supporters, actress Jane Fonda and her husband Tom Hayden, apparently just to recall for Californians who the governor's friends are. Other Wilson spots boost the mayor's past accomplishments; they are long on r,esum,e but short on vision.

If Brown does win, it will probably have less to do with his earlier spaceship-Earth-and-seaweed-salad view of the world than with the New Deal politics of FDR. The issues Brown emphasizes in both the paid and free media are jobs and his unqualified support of Social Security.